Tool and method of reflow

ABSTRACT

A tool and a method of reflow are provided. In various embodiments, the tool includes a chamber unit, a wafer lifting system, a heater, and an exhausting unit. The wafer lifting system is disposed in the chamber unit. The heater is coupled to the chamber unit, and configured to heat the wafer. The exhausting unit coupled to the chamber unit, and configured to exhaust gas in the chamber unit. The wafer lifting system is configured to receive and move the wafer in the chamber unit, and to provide a vertical distance between the heater and the wafer in the chamber unit.

BACKGROUND

When electronic products are becoming smaller in size and moreintelligent with a high performance and a high reliability, requirementsto integrated circuit (IC) package techniques are accordingly increasedfor higher integration of IC. Among these IC package techniques, waferbumping is used to form solder bumps over an entire wafer on whichintegrated circuits have been built. After the wafer bumping process,the wafer is cut into individual chips for inner lead bonding. The waferbumping is a critical step for device packaging, because the bumpsformed on the wafer serve as electrical, mechanical, and mountingconnections for flip-chip assemblies. These bumps must exhibit superioradhesion to the chips and minimum electrical resistance.

The bumps are formed by depositing solder alloy onto metal pads of thewafer. The deposited solder alloy is then performed a reflow process toreflow at a certain thermal profile including temperature above itsmelting point, form a metallic interconnect with the chips, and convertfrom its as-plated form into a spherical shape driven by liquid surfacetension. Besides, the deposited solder alloy typically contains a nativemetal oxide layer on its surface. When the solder alloy is melted, themetal oxide layer remains in solid phase and acts as a skin. Thisconstrains the molten solder surface and hinders the formation ofuniform, spherical bumps. Therefore, it is also important to removesurface oxides from the deposited solder during the reflow process.

As aforementioned, since requirements to wafer bumping techniques areincreased and higher, the thermal profile controlling and the metaloxide removal of the solder alloy during the reflow process have to bewell controlled. Accordingly, improvements in reflow tools and methodsof reflow continue to be sought.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic diagram illustrating a portion of a reflow toolaccording to various embodiments of the present disclosure.

FIG. 2 is a top view of a portion of the reflow tool illustrated in FIG.1.

FIG. 3 is a schematic diagram illustrating a portion of a reflow toolaccording to various embodiments of the present disclosure.

FIG. 4 is a schematic top-view illustrating the reflow tool according tovarious embodiments of the present disclosure.

FIG. 5 is a flowchart illustrating a method of fluxless reflow accordingto various embodiments of the present disclosure.

FIG. 6 is a schematic diagram of a thermal profiling illustrating themethod of fluxless reflow according to various embodiments of thepresent disclosure.

FIG. 7 is a schematic top-view illustrating the reflow tool according tovarious embodiments of the present disclosure.

FIG. 8 is a schematic diagram of another thermal profiling illustratingthe method of fluxless reflow according to various embodiments of thepresent disclosure.

FIG. 9 is a schematic diagram illustrating a portion of a reflow toolaccording to various embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

The singular forms “a,” “an” and “the” used herein include pluralreferents unless the context clearly dictates otherwise. Therefore,reference to, for example, a liner layer includes embodiments having twoor more such liner layers, unless the context clearly indicatesotherwise. Reference throughout this specification to “one embodiment”or “an embodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present disclosure. Therefore, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Further, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments. It should be appreciated that the followingfigures are not drawn to scale; rather, these figures are intended forillustration.

Since the thermal profile of the solder alloy during the reflow processhas to be well controlled, large space of a reflow tool is oftenrequired to provide multiple thermal zones for the wafer to travel.Therefore, footprint design of numerous reflow tools is large. The costof settling a reflow tool is accordingly increased. In this regard,reflow tools and methods of soldering are provided according to variousembodiments of the present disclosure.

FIG. 1 is a schematic diagram illustrating a portion of a reflow toolaccording to various embodiments of the present disclosure. Asillustrated in FIG. 1, the reflow tool 100 includes a chamber unit 110,a wafer lifting system 120, a heater 130, and an exhausting unit 150.The chamber unit 110 is configured to perform the reflow process on thewafer 180. Flip chip is a technique in which a chip is flipped over andthen connected with a board by solder balls formed on the surface of thechip so as to reduce the package size. The flip chip technology maysatisfy the requirement for high performance with a smaller size. Bumpfabrication is a key technique in flip chip technology. The bump is ametal solder ball formed by depositing solder over an interconnectionmetal layer of a chip and reflowing at a certain temperature. Processesfor bump fabrication could start from providing a wafer. The wafer has asurface with a passivation layer and an interconnection metal layer. Anunder-bump metallurgy (UBM) layer is formed on the surface of the wafer.Next, a photoresist layer is coated over the UBM layer, and is subjectedto exposure and development so as to form a photoresisit opening. Solderalloy for bump is deposited over the photoresist opening. Then thephotoresisit layer and part of the UBM layer are removed. Flux isapplied over the surface of the wafer, and is reflowed at a certaintemperature to form a solder ball as the bump. Then, the flux on thebump and over the surface of the wafer is removed. The typical fluxconsists of colophony resin, active agent, solvent, thixotropic agentand other additives. In the some reflow process, the flux is mainly usedto remove contaminations on the solder surface, deoxidize metal oxides,and facilitate the reflow; in the some reflow process, the bump having adesired shape is formed by using the flux and controlling thetemperature of the reflow. The reflow process may be a flux reflowprocess. Flux is a reducing agent designed to help reduce metal oxidesat the points of solder contact to improve the electrical connection andmechanical strength of solders on the wafer 180. The two principal typesof flux are acid flux and rosin flux. The acid flux is used for metalmending and plumbing, and the rosin flux is used in electronics wherethe corrosiveness of acid flux and vapors released when solder is heatedwould risk damaging delicate circuitry. Due to concerns over atmosphericpollution and hazardous waste disposal, the electronics industry hasbeen gradually shifting from the flux reflow process to a fluxlessreflow process. In the fluxless reflow process, the flux is replaced bya deoxidizing gas. Similarly, the deoxidizing gas is a reducing agentdesigned to help reduce metal oxides at the points of solder contact toimprove the electrical connection and mechanical strength of solders onthe wafer 180.

Referring to FIG. 1, the wafer lifting system 120 is disposed in thechamber unit 110. The wafer lifting system 120 is configured to receiveand move the wafer 180 in the chamber unit 110 during the reflowprocess. The heater 130 is coupled to the chamber unit 110, andconfigured to heat the wafer 180 during the reflow process. Asillustrated in FIG. 1, in various embodiments of the present disclosure,the heater 130 is disposed above the chamber unit 110. It should benoticed that the wafer lifting system 120 is configured to receive andmove the wafer 180 in the chamber unit 110, and to provide a verticaldistance d between the heater 130 and the wafer 180 in the chamber unit110. As illustrated in FIG. 1, in various embodiments of the presentdisclosure, the wafer lifting system 120 includes a wafer holder 122 anda lifting pin 124. The wafer holder 122 is configured to receive thewafer 180 and the lifting pin 124 is coupled to the wafer holder 122 andconfigured to move the wafer 180 in the chamber unit 110. In variousembodiments of the present disclosure, the lifting pin 124 movesvertically to provide the vertical distance d between the heater 130 andthe wafer 180 in the chamber unit 110. The vertical distance d affectstemperature of the wafer 180. As aforementioned, various temperaturesare required to pre-wet, soak, melt, and cool the solder alloy duringthe reflow process. In other words, a proper thermal profile of thewafer 180 is required to be form by the reflow process. As illustratedin FIG. 1, the vertical distance d is decreasing when the wafer liftingsystem 120 is elevating the wafer 180, and the temperature of the wafer180 is accordingly increasing while the vertical distance d isdecreasing. On the other hand, the vertical distance d is increasingwhen the wafer lifting system 120 is lowering the wafer 180, and thetemperature of the wafer 180 is accordingly decreasing while thevertical distance d is increasing. Therefore, the thermal profile of thewafer 180 could be controlled by the wafer lifting system 120. Invarious embodiments of the present disclosure, the lifting pin 124 ofthe wafer lifting system 120 is capable to move vertically to providethe vertical distance d between the heater 130 and the wafer 180 in thechamber unit 110. Accordingly, the thermal profile of the wafer 180could be controlled in a flexible way. In other words, it is notnecessary for the reflow tool 100 according to various embodiments ofthe present disclosure to have the heaters with various temperatures,and therefore a smaller footprint than those have the heaters withvarious temperatures is required. Accordingly, less space is required tosettle the reflow tool 100 in a factory, and the cost of settling thereflow tool could be further reduced. In addition, the wafer 180 ismoved by the wafer lifting system 120 of the reflow tool 100 instead ofputting on a transferring belt with inert gas purge of numerous reflowtools. Therefore, the wafer 180 could be moved precisely and smoothly bythe wafer lifting system 120, and risks of vibration during the reflowprocess could be eliminated. Accordingly, failure of solder connectioncould be also improved.

Referring to FIG. 1 and FIG. 2, FIG. 2 is a top view of a portion of thereflow tool illustrated in FIG. 1. The exhausting unit 150 is coupled tothe chamber unit 110, and configured to exhaust gas 190 in the chamberunit 110. The gas 190 could be generated during the reflow process. Asillustrated in FIG. 1, in various embodiments of the present disclosure,the heater 130 is disposed above the chamber unit 110, and the heater130 has a plurality of slits 136. The exhausting unit 150 is disposed onthe heater 130. The exhausting unit 150 exhausts gas 190 in the chamberunit 110 through the plurality of slits 136. It should be notice thatthe exhausting unit 150 is disposed above the wafer 180, and configuredto exhaust gas 190 in the chamber unit 110 during the reflow process.Therefore, the gas 190 flows upward from the surface of wafer 180.Accordingly, risk of particles depositing on the wafer 180 could befurther reduced, and yield of the wafer 180 in the reflow process couldbe further improved.

Referring to FIG. 1 again, in various embodiments of the presentdisclosure, the reflow tool further includes a jet system 140 coupled tothe chamber unit, and configured to jet a deoxidizing gas 142 on thewafer 180. As aforementioned, flux is a reducing agent designed to helpreduce metal oxides at the points of solder contact to improve theelectrical connection and mechanical strength of solders on the wafer180. Due to concerns over atmospheric pollution and hazardous wastedisposal, the electronics industry has been gradually shifting from theflux reflow process to the fluxless reflow process. In the fluxlessreflow process, the deoxidizing gas 142 is the reducing agent designedto reduce metal oxides at the points of solder contact to improve theelectrical connection and mechanical strength of solders on the wafer180, and is jetted to the solders on the wafer 180 by the jet system 140during reflow process. In various embodiments of the present disclosure,the deoxidizing gas 142 could be hydrogen gas, formic acid gas, or acombination thereof. By-products generated by redox reaction between thesolders on the wafer 180 and the deoxidizing gas 142 during the fluxlessreflow process are relatively clean, non-toxic, and could be easilyvented out of the chamber unit 110 by the exhausting unit 150. Asillustrated in FIG. 1, in various embodiments of the present disclosure,the jet system 140 is disposed on two opposite sidewalls 111 and 113 ofthe chamber unit 110 to jet the deoxidizing gas 142 into the chamberunit 110. Therefore, a relative balance condition of jetting thedeoxidizing gas 142 could be obtain, and vibration of the wafer 180during the fluxless reflow process could be reduced. Accordingly, riskof bumping fail could be further improved. However, the presentdisclosure is not limited thereto. The jet system 140 could be designedin any proper shape and disposed on any proper positions to form abalance condition of jetting the deoxidizing gas 142 of the wafer 180.

FIG. 3 is a schematic diagram illustrating a portion of a reflow toolaccording to various embodiments of the present disclosure. FIG. 4 is aschematic top-view illustrating the reflow tool according to variousembodiments of the present disclosure. As illustrated in FIG. 3 and FIG.4, in various embodiments of the present disclosure, the chamber unit110 includes an inner cylindrical shield 114 and an outer cylindricalshield 112. The inner cylindrical shield 114 and the outer cylindricalshield 112 constitute the chamber unit 110 as a ring shape chamber unit.The wafer lifting system 120 in the chamber unit 110 moves in a circularmotion as shown in FIG. 4. Therefore, as illustrated in FIG. 3, thewafer 180 is moved by the wafer lifting system 120 in the circularmotion during the reflow process. It should be noticed that the waferlifting system 120 does not only provide the vertical distance betweenthe heater 130 and the wafer 180 in the chamber unit 110, but also movesthe wafer 180 in the circular motion during the reflow process.Therefore, the wafer 180 is moved in a spiral trace by the wafer liftingsystem 120 as shown in FIG. 3. In some embodiments of the presentdisclosure, the chamber unit 110 is covered by the heater 130, and theheater 130 is employed to provide a substantially uniform temperature.For example, three temperature zones 131,132 and 133 have substantiallythe same temperature as illustrated in FIG. 3. Therefore, thetemperature of the wafer 180 could be only affected by the verticaldistance between the heater 130 and the wafer 180. In variousembodiments of the present disclosure, the vertical distance between theheater 130 and the wafer 180 in the chamber unit 110 further includes areducing distance section, a constant distance section, and anincreasing distance section. As illustrated in FIG. 3, in the reducingdistance section, the vertical distance is decreasing when the waferlifting system 120 is elevating the wafer 180 in a thermal zone 115 ofthe chamber unit 110, and the temperature of the wafer 180 isaccordingly increasing while the vertical distance is decreasing; in theconstant distance section, the vertical distance is constant when thewafer lifting system 120 is not elevating or lowering the wafer 180 in athermal zone 116 of the chamber unit 110, and the temperature of thewafer 180 is accordingly constant while the vertical distance isconstant; and in the increasing distance section, the vertical distanceis increasing when the wafer lifting system 120 is lowering the wafer180 in a thermal zone 117 of the chamber unit 110, and the temperatureof the wafer 180 is accordingly decreasing while the vertical distanceis increasing. In some other embodiments of the present disclosure, thechamber unit 110 is covered by the heater 130, and the heater 130 has aplurality of temperature zones. For example, three temperature zones131,132 and 133 have different temperatures as illustrated in FIG. 3.The temperature of the wafer 180 could not only be affected by thevertical distance between the heater 130 and the wafer 180, but also beaffected by different temperature zones 131, 132 and 133 of the heater130. It should be noticed that since the wafer lifting system 120 in thechamber unit 110 provides the vertical distance between the heater 130and the wafer 180 in the chamber unit 110 and also moves in the circularmotion, a thermal profile of the wafer 180 for the reflow process couldbe formed when the wafer 180 is moved in a circle path as illustrated inFIG. 3 and FIG. 4. Therefore, the reflow tool 200 according to variousembodiments of the present disclosure requires a smaller footprint thanthose with a straight path for the wafer to move. Accordingly, lessspace is required to settle the reflow tool 200 in a factory, and thecost of settling the reflow tool could be further reduced. In addition,the wafer 180 is moved by the wafer lifting system 120 of the reflowtool 200 instead of putting on a transferring belt with inert gas purgeof numerous reflow tools. Therefore, the wafer 180 could be movedprecisely and smoothly by the wafer lifting system 120, and risks ofvibration during the reflow process could be eliminated. Accordingly,failure of solder connection could be also improved. Also illustrated inFIG. 3, in various embodiments of the present disclosure, the reflowtool 200 further includes a buffer zone 160 and at least one frontopening unified pod 210. The buffer zone 160 is coupled to the chamberunit 110. The front opening unified pod 210 is coupled to the bufferzone 160. The buffer zone 160 is configured to transfer the wafer 180between the front opening unified pod 210 and the wafer lifting system120. As illustrated in FIG. 4, in various embodiments of the presentdisclosure, the buffer zone 160 includes a first buffer zone 162 and asecond buffer zone 164. The first buffer zone 162 is coupled to thechamber unit 110, and configured to transfer the wafer 180 from thefront opening unified pod 210 to the wafer lifting system 120. Thesecond buffer zone 164 is coupled to the chamber unit 110, andconfigured to transfer the wafer 180 from the wafer lifting system 120to the front opening unified pod 210. Therefore, two buffer zones (oneis input and the other one is output) could further improve processefficiency (wafer per hour, WPH) of the reflow tool 200 while the wafers180 are processed in a continuous process as illustrated in FIG. 3.

FIG. 5 is a flowchart illustrating a method 500 of fluxless reflowaccording to various embodiments of the present disclosure. The method500 begins with block 502 in which a wafer is transferred to a chamberunit of a reflow tool. A vertical distance between the wafer and aheater of the reflow tool is formed. The method 500 continues with block504 in which the vertical distance is reduced. The operation of reducingthe vertical distance is performed in a first period. The method 500also includes keeping the vertical distance in a second period as shownin block 506, and increasing the vertical distance, wherein theoperation of increasing the vertical distance is performed in a thirdperiod as shown in block 510. It should be noticed that a jet system ofthe reflow tool jets a deoxidizing gas during the operation of reducingthe vertical distance and the operation of keeping the vertical distancein the second period. As aforementioned, the deoxidizing gas is thereducing agent designed to reduce metal oxides at the points of soldercontact to improve the electrical connection and mechanical strength ofsolders on the wafer, and is jetted to the solders on the wafer by thejet system during the reflow process. In various embodiments of thepresent disclosure, between the operation of keeping the verticaldistance in the second period and the operation of increasing thevertical distance, the method 500 further includes reducing the verticaldistance, wherein the operation of reducing the vertical distance isperformed in a fourth period as shown in block 508. In variousembodiments of the present disclosure, the operations of reducing thefirst distance to a second distance, keeping the second distance for asecond period, and increasing the second distance to a third distanceare performed by a wafer lifting system of the reflow tool. The waferlifting system includes a wafer holder configured to receive the waferand a lifting pin coupled to the wafer holder. The wafer lifting systemis configured to vertically move the wafer. The wafer lifting system iscapable to move in a circular motion in the chamber unit, and the firstperiod, second period and the third period are controlled by the waferlifting system. The details of the method 500 are described in FIG. 6and following paragraphs.

FIG. 6 is a schematic diagram of a thermal profiling illustrating themethod of fluxless reflow according to various embodiments of thepresent disclosure. Referring to FIG. 6 and FIG. 3, after the wafer 180is transferred to the chamber unit 110 of the reflow tool 200. Thevertical distance d1 between the wafer 180 and the heater 130 of thereflow tool 200 is formed. The initial temperature of the wafer 180 is,for example, T1 as illustrated in FIG. 6. Next, the vertical distance d1is reduced such that the temperature of the wafer 180 is accordinglyincreased. For example, the temperature of the wafer 180 could beincreased from T1 to T2 as illustrated in FIG. 6. Also shown in FIG. 3,the operation of reducing the vertical distance d1 could be performed inthe thermal zone 115 of the chamber unit 110 of the reflow tool 200. Theoperation of reducing the vertical distance d1 is performed in a firstperiod t1. The first period t1 is to preheat and establish a ramp-uprate of the temperature of the wafer 180. As illustrated in FIG. 6, theramp-up rate is a temperature/time slope in the thermal zone 115. Itrepresents how fast the temperature of the wafer 180 changes. Theramp-up rate is, for example, between 0.5° C. and 5.0° C. per second.However, the present disclosure is not limited to it. The ramp-up ratecould be properly controlled by the wafer lifting system 120, thetemperature of the heater 130, the velocity of the circular motion ofthe wafer lifting system 120 (as illustrated in FIG. 3), or combinationsthereof according to various solder materials applied on the wafer 180or other process criteria. The jet system of the reflow tool 200 jetsthe deoxidizing gas to reduce surface tension of the solders on thewafer 180 for metallurgical bonding in the following operation.

Continually referring to FIG. 6, the vertical distance d2 is kept in asecond period t2 such that the temperature of the wafer 180 isaccordingly constant. For example, the temperature of the wafer 180could be T2 as illustrated in FIG. 6. Also shown in FIG. 3, theoperation of keeping the vertical distance d2 in a second period t2could be performed in the thermal zone 116 of the chamber unit 110 ofthe reflow tool 200. Solders on the wafer 180 reflow in the secondperiod t2, and the second period t2 is the part of the reflow processwhere the maximum temperature is reached. The jet system of the reflowtool 200 jets the deoxidizing gas to reduce surface tension of thesolders on the wafer 180 to accomplish metallurgical bonding.

Continually referring to FIG. 6, the vertical distance d2 between thewafer 180 and the heater 130 of the reflow tool 200 is increased suchthat the temperature of the wafer 180 is accordingly decreased. Forexample, the temperature of the wafer 180 could be decreased from T2 toT1 as illustrated in FIG. 6. Also shown in FIG. 3, the operation ofincreasing the vertical distance, for example, from d2 to d3, could beperformed in the thermal zone 117 of the chamber unit 110 of the reflowtool 200. The operation of increasing the vertical distance is performedin a third period t3. As illustrated in FIG. 6, the ramp-down rate is atemperature/time slope in the thermal zone 117. It represents how fastthe temperature of the wafer 180 changes. In the third period t3,temperature of the wafer 180 is gradually cooled, and the solder jointson the wafer 180 are solidified. Proper cooling inhibits excessinter-metallic formation or thermal shock to the components of the wafer180. The ramp-down rate is, for example, between 2.0° C. and 6.0° C. persecond. However, the present disclosure is not limited to it. Theramp-down rate could be properly controlled by the vertical distancecontrolled by the wafer lifting system 120, the temperature of theheater 130, the velocity of the circular motion of the wafer liftingsystem 120 (as illustrated in FIG. 3), or combinations thereof accordingto various solder materials applied on the wafer 180 or other processcriteria.

FIG. 7 is a schematic top-view illustrating the reflow tool according tovarious embodiments of the present disclosure, and FIG. 8 is a schematicdiagram of another thermal profiling illustrating the method of fluxlessreflow according to various embodiments of the present disclosure.Referring to FIG. 7 and FIG. 8, after the wafer 180 is transferred tothe chamber unit 110 of the reflow tool 200. The vertical distance d1between the wafer 180 and the heater 130 of the reflow tool 100 isformed. As illustrated in FIG. 8, the initial temperature of the wafer180 is, for example, T1. Next, the vertical distance d1 is reduced suchthat the temperature of the wafer 180 is accordingly increased. Forexample, the temperature of the wafer 180 could be increased from T1 toT2 as illustrated in FIG. 8. Also shown in FIG. 7, the operation ofreducing the vertical distance d1 could be performed in the thermal zone115 of the chamber unit 110 of the reflow tool 200. Also shown in FIG.8, the operation of reducing the vertical distance d1 is performed in afirst period t1. The first period t1 is to preheat and establish aramp-up rate of the temperature of the wafer 180. The details ofpreheating and establishing the ramp-up rate of the temperature of thewafer 180 are similar to those described in FIG. 6, and therefore thedetails are omitted here. The ramp-up rate could be properly controlledby the wafer lifting system 120, the temperature of the heater 130, thevelocity of the circular motion of the wafer lifting system 120 (asillustrated in FIG. 7), or combinations thereof according to varioussolder materials applied on the wafer 180 or other process criteria.

Continually referring to FIG. 8, the vertical distance d2 is kept in asecond period t2 such that the temperature of the wafer 180 isaccordingly constant. For example, the temperature of the wafer 180could be T2 as illustrated in FIG. 8. Also shown in FIG. 7, theoperation of keeping the vertical distance d2 in a second period t2could be performed in the thermal zone 116 of the chamber unit 110 ofthe reflow tool 200. Solders on the wafer 180 are thermally soaked, andthe deoxidizing gas jetted from the jet system of the reflow tool 200reduces surface tension of the solders on the wafer 180 to start beginoxide reduction of solders on the wafer 180. If temperature T2 is toohigh, solder spattering might be induced and the following operationsmight be impacted. On the other hand, the deoxidizing gas may not fullyactivate to begin oxide reduction of solders on the wafer 180 iftemperature T2 is too low.

Continually referring to FIG. 8, the vertical distance is furtherreduced such that the temperature of the wafer 180 is accordinglyincreased, for example, from d2 to d3. Also shown in FIG. 7, theoperation of reducing the vertical distance could be performed in thethermal zone 117 of the chamber unit 110 of the reflow tool 200. Asshown in FIG. 8, the operation of reducing the vertical distance isperformed in a fourth period t4. The fourth period t4 is to reflow andestablish a ramp-up rate of the temperature of the wafer 180. Thedetails of reflowing are similar to those described in FIG. 6, andtherefore the details are omitted here. The difference between FIG. 8and FIG. 6 is that another ramp-up rate is formed as thetemperature/time slope in the thermal zone 117 in FIG. 8. It representshow fast the temperature of the wafer 180 changes. Solders on the wafer180 reflow in the fourth period t4, and the fourth period t4 is the partof the reflow process where the maximum temperature, for example, T3 isreached. The jet system of the reflow tool 200 jets the deoxidizing gasto reduce surface tension of the solders on the wafer 180 to accomplishmetallurgical bonding. The ramp-up rate could also be properlycontrolled by the wafer lifting system 120, the temperature of theheater 130, and the velocity of the circular motion of the wafer liftingsystem 120 (as illustrated in FIG. 7).

Continually referring to FIG. 8, the vertical distance between the wafer180 and the heater 130 of the reflow tool 100 is increased (from d3 tod4), such that the temperature of the wafer 180 is accordinglydecreased. For example, the temperature of the wafer 180 could bedecreased from T3 to T1 as illustrated in FIG. 8. Also shown in FIG. 7,the operation of increasing the vertical distance, for example, from d3to d4, could be performed in the thermal zone 118 of the chamber unit110 of the reflow tool 200. The operation of increasing the verticaldistance is performed in a third period t3. As illustrated in FIG. 8,the ramp-down rate is a temperature/time slope in the thermal zone 118.It represents how fast the temperature of the wafer 180 changes. In thethird period t3, temperature of the wafer 180 is gradually cooled, andthe solder joints on the wafer 180 are solidified. The details ofcooling are similar to those described in FIG. 6, and therefore thedetails are omitted here.

FIG. 9 is a schematic diagram illustrating a portion of a reflow tool300 according to various embodiments of the present disclosure. Asillustrated in FIG. 9, the reflow tool 300 for the wafer 180 includesthe chamber unit 110, a wafer moving system 220, a heater 230, the jetsystem (not shown), and the exhausting unit (not shown). The chamberunit 110, the jet system, and the exhausting unit are similar to thosedescribed above, and therefore the details are omitted here. Thedifference is that the heater 230 has a plurality of temperature zones231, 232, and 233 to form a plurality of thermal zones 115, 116, and 117in the chamber unit 110. The wafer moving system 220 is configured toreceive and move the wafer 180 through the plurality of thermal zones115, 116, and 117 in a circular motion. Therefore, the reflow tool 300according to various embodiments of the present disclosure requires asmaller footprint than those with a straight path for the wafer to move.Accordingly, less space is required to settle the reflow tool 300 in afactory, and the cost of settling the reflow tool could be furtherreduced. In addition, the wafer 180 is moved by the wafer moving system220 of the reflow tool 300 instead of putting on a transferring beltwith inert gas purge of numerous reflow tools. Therefore, the wafer 180could be moved precisely and smoothly by the wafer moving system 220,and risks of vibration during the reflow process could be eliminated. Invarious embodiments of the present disclosure, the wafer moving system220 includes a wafer holder 222 and a lifting pin 224. The wafer holder222 is configured to receive the wafer 180. The lifting pin 224 iscoupled to the wafer holder 222, and configured to move the wafer 180 inthe chamber unit 110. In various embodiments of the present disclosure,the lifting pin 224 moves vertically to provide a vertical distancebetween the heater 230 and the wafer 180 in the chamber unit 110.

According to various embodiments of the present disclosure, the waferlifting system of the reflow tool is capable to move vertically toprovide the vertical distance between the heater and the wafer in thechamber unit. Accordingly, the thermal profile of the wafer could becontrolled in a flexible way. Therefore, it is not necessary for thereflow tool according to various embodiments of the present disclosureto have the heaters with various temperatures, and therefore a smallerfootprint than those have the heaters with various temperatures isrequired. It results in less space is required to settle the reflow toolin a factory, and the cost of settling the reflow tool could be furtherreduced. In addition, the wafer is moved by the wafer lifting system ofthe reflow tool instead of putting on a transferring belt with inert gaspurge. Therefore, the wafer could be moved precisely and smoothly by thewafer lifting system, and risks of vibration during the reflow processcould be eliminated. Accordingly, failure of solder connection could bealso improved. Furthermore, in some embodiments of the presentdisclosure, the wafer is moved in a circle path as illustrated in FIGS.3, 4 and 7-9. Therefore, the reflow tool according to some embodimentsof the present disclosure requires a smaller footprint than those with astraight path for the wafer to move. Accordingly, even less space isrequired to settle the reflow tool in a factory, and the cost ofsettling the reflow tool could be significantly reduced. In someembodiments of the present disclosure, the jet system could be designedin any proper shape and disposed on any proper positions to form abalance condition of jetting the deoxidizing gas of the wafer. In someembodiments of the present disclosure, the exhausting unit is disposedabove the wafer, and configured to exhaust gas in the chamber unitduring the reflow process. Therefore, the gas flows upward from thesurface of wafer, and the risk of particles depositing on the wafercould be further reduced. In some embodiments of the present disclosure,two buffer zones coupled to the chamber unit could further improveprocess efficiency (wafer per hour, WPH) of the reflow tool while thewafers are processed in a continuous process.

In various embodiments of the present disclosure, the reflow tool for awafer includes a chamber unit, a wafer lifting system, a heater, and anexhausting unit. The wafer lifting system is disposed in the chamberunit. The heater is coupled to the chamber unit, and configured to heatthe wafer. The exhausting unit coupled to the chamber unit, andconfigured to exhaust gas in the chamber unit. The wafer lifting systemis configured to receive and move the wafer in the chamber unit, and toprovide a vertical distance between the heater and the wafer in thechamber unit.

In various embodiments of the present disclosure, the reflow tool for awafer includes a chamber unit, a wafer moving system, a heater, a jetsystem, and an exhausting unit. The wafer moving system is disposed inthe chamber unit. The heater is coupled to the chamber unit, andconfigured to heat the wafer. The jet system is coupled to the chamberunit, and configured to jet a deoxidizing gas on the wafer. Theexhausting unit is coupled to the chamber unit, and configured toexhaust gas in the chamber unit. The heater has a plurality oftemperature zones to form a plurality of thermal zones in the chamberunit, the wafer moving system is configured to receive and move thewafer through the plurality of thermal zones in a circular motion.

In various embodiments of the present disclosure, the method of reflowincludes transferring a wafer to a chamber unit of a reflow tool,wherein a vertical distance between the wafer and a heater of the reflowtool is formed. The method further includes reducing the verticaldistance, wherein the operation of reducing the vertical distance isperformed in a first period. The method further includes keeping thevertical distance in a second period. The method further includesincreasing the vertical distance, wherein the operation of increasingthe vertical distance is performed in a third period. A jet system ofthe reflow tool jets a deoxidizing gas during the operation of reducingthe vertical distance and the operation of keeping the vertical distancein the second period.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A tool comprising: a ring shape chamber unithaving an inner cylindrical wall and an outer cylindrical wall, whereinthe inner cylindrical wall and the outer cylindrical wall defines thering shape chamber; a wafer lifting system disposed in the ring shapechamber, wherein the wafer lifting system comprises a wafer holderconfigured to support a wafer and a lifting pin coupled to the waferholder; a heater coupled to the ring shape chamber unit, and configuredto heat the wafer; and an exhausting unit coupled to the ring shapechamber unit, and configured to exhaust gas in the ring shape chamber,wherein the heater is disposed between the exhausting unit and the waferlifting system, and the wafer lifting system is configured to move thewafer in a spiral motion and to provide varying vertical distancebetween the heater and the wafer by vertically moving the lifting pin asthe wafer lifting system moves in a spiral motion within the ring shapechamber.
 2. The tool of claim 1, further comprising a jet system coupledto the ring shape chamber unit, and configured to jet a deoxidizing gason the wafer.
 3. The tool of claim 2, wherein the jet system is disposedon the inner cylindrical wall and the outer cylindrical wall of the ringshape chamber unit to jet the deoxidizing gas into the ring shapechamber.
 4. The tool of claim 1, wherein the ring shape chamber unitcomprises: a first thermal zone, a second thermal zone and a thirdthermal zone which are disposed side by side in the ring shape chamberto form a circle.
 5. The tool of claim 1, wherein the heater is disposedabove the ring shape chamber unit.
 6. The tool of claim 5, wherein thering shape chamber unit is covered by the heater.
 7. The tool of claim6, wherein the heater has a plurality of temperature zones.
 8. The toolof claim 5, wherein the heater has a plurality of slits, and theexhausting unit is configured to exhaust gas in the ring shape chamberthrough the plurality of slits.
 9. The tool of claim 1, furthercomprising: a buffer zone coupled to the ring shape chamber unit; and atleast one front opening unified pod coupled to the buffer zone, whereinthe buffer zone is configured to transfer the wafer between the frontopening unified pod and the wafer lifting system.
 10. The tool of claim9, wherein the buffer zone comprises: a first buffer zone coupled to thering shape chamber unit, and configured to transfer the wafer from thefront opening unified pod to the wafer lifting system; and a secondbuffer zone coupled to the ring shape chamber unit, and configured totransfer the wafer from the wafer lifting system to the front openingunified pod.
 11. A tool comprising: a ring shape chamber unit having aninner cylindrical wall and an outer cylindrical wall, wherein the innercylindrical wall and the outer cylindrical wall defines a ring shapechamber; a wafer lifting system disposed in the ring shape chamber,wherein the wafer lifting system comprises a wafer holder configured tosupport a wafer and a lifting pin coupled to the wafer holder; a heatercoupled to the ring shape chamber unit, and configured to heat thewafer; a jet system coupled to the ring shape chamber unit, andconfigured to jet a deoxidizing gas on the wafer; and an exhausting unitcoupled to the ring shape chamber unit, and configured to exhaust gas inthe ring shape chamber, wherein the heater is disposed between theexhausting unit and the wafer lifting system, and the wafer liftingsystem is configured to move the wafer in a spiral motion and to providevarying vertical distance between the heater and the wafer by verticallymoving the lifting pin as the wafer lifting system moves in a spiralmotion within the ring shape chamber.
 12. A tool comprising: a ringshape chamber unit having an inner cylindrical wall and an outercylindrical wall, wherein the inner cylindrical wall and the outercylindrical wall defines a ring shape chamber; at least one frontopening unified pod coupled to the ring shape chamber unit; a waferlifting system disposed in the ring shape chamber, wherein the waferlifting system comprises a wafer holder configured to support a waferand a lifting pin coupled to the wafer holder; a heater coupled to thering shape chamber unit, and configured to heat the wafer; and anexhausting unit configured to exhaust gas in the ring shape chamber,wherein the heater is disposed between the exhausting unit and the waferlifting system, wherein the wafer lifting system is configured to movethe wafer in a spiral motion and to provide varying vertical distancebetween the heater and the wafer by vertically moving the lifting pin asthe wafer lifting system moves in a spiral motion within the ring shapechamber.
 13. The tool of claim 12, further comprising a buffer zoneconnected to the front opening unified pod and the ring shape chamber.14. The tool of claim 13, wherein the lifting pin is further movable inthe buffer zone.
 15. The tool of claim 13, wherein the buffer zonecomprises: an input buffer zone; and an output buffer zone adjacent tothe input buffer zone.